1. Field of the Invention
This invention relates to an ink composition especially suited for ink-jet recording, a process for its preparation, and an ink-jet recording process.
2. Description of the Related Art
Ink-jet recording is a system in which ink droplets are formed by ink ejection methods of various types (e.g., a system utilizing electrostatic attraction, a system in which mechanical vibration or displacement is imparted to ink by the use of a piezoelectric device, and a system in which ink is heated to cause it to bubble and a pressure produced when it bubbles is utilized), and part or the whole of them is caused to adhere to recording mediums such as paper to make a record.
As ink compositions used in such ink-jet recording systems, those prepared by dissolving or dispersing a water-soluble dye or a pigment in water or an aqueous medium comprising water and a water-soluble organic solvent are known and put into use. Such ink compositions are required to have various performances most suited for what they are used. For example, they are required to cause no precipitation or aggregation even when unused for a long period of time, to cause no clogging at nozzles and in ink channels of the head of an ink-jet printer and to ensure good print quality. In particular, the performance most required is the liquid stability that the ink composition does not cause clogging of, and deposits at, nozzles and ink channels of the ink-jet printer head when recording is performed using the ink composition and also when the recording is stopped over a long period of time. Among the ink-jet recording systems, the ink-jet recording system that utilizes heat energy tends to cause deposition of foreign matter on the surface of its heating element as a result of temperature changes, and the problem is especially important.
In conventional ink compositions, however, some additives are necessary to meet various conditions such as ink ejection conditions, long-term storage stability, sharpness and density of images at the time of recording, surface tension, electrical properties and so forth. Such additives, and also dyes used in the ink compositions, contain various impurities, and hence have brought about the problems such that they cause the clogging of nozzles and ink channels of the ink-jet printer head, and cause deposits during long-term storage. In the ink-jet recording system that utilizes heat energy, such impurities have also caused the problem that deposits are formed on the surface of the heating element.